Many trace elements found on these space travelers are nearly impossible to find on Earth.Rocks can be: (1) made of minerals, each of which has a specific crystal structure and chemical composition (2) made of pieces of other rocks (3) glassy (like obsidian) or, (4) contain material made by living organisms (for example coal, which contains carbon from plants). The key thing to remember about meteorites is that they have much different percentages of elements than rocks on Earth. You will also find many smaller trace elements. Meteorites are mainly made of iron and nickel. They look just like rocks until you break them open. There are also millions of tiny meteorites. Most scientists now believe that a super-massive meteorite hit the Earth and created an extinction event for the dinosaurs. Some super big ones have created massive craters across the globe. Sure you can debate whether a meteorite is a rock, but you definitely find them all over the Earth. That's right, not all rocks are from Earth. Examples of sedimentary rock include sandstone, amber, anthracite, and limestone. That compacted sediment eventually becomes a type of rock. Now if you watch this happen over millions of years, more and more sediment builds up and compacts. When that material gets to the beach, it sits there. It could be in a flood plain or a valley, but we're using a coastline as an example. That sediment and silt runs downstream and deposits where the river ends. A river flows through a canyon and picks up a bunch of silt. Sedimentary rock types are created when sediment compresses. The last of the big three rock types is probably the rarest. Over time, because of the movement of the crust, these metamorphic rocks are pushed to the surface where you can find them every day. They are also found near fault lines where plates push against each other and create enormous pressures. Because pressure and heat are involved, these rock types are usually found deep beneath the surface. Some examples are marble, jade, slate, and gneiss. Some force (heat/pressure) has changed these rocks from one type into a new type. Look at the name 'metamorphic.' It looks like the word used to describe insects that go through a metamorphosis. The heat from the magma changes all of the rock around it. You often find metamorphic rock near volcanoes and sources of super hot rock. Even though heat is involved, they didn't start off as molten rock. This rock type is created by heat and/or pressure. Some examples of igneous rock are granite, all volcanic rock, basalt, and obsidian. The intrusive types are usually found in areas called plutons and dikes, big old pools of molten rock that were just beneath the surface. If you walk around a volcano, you will find those extrusive types. These igneous types have all hardened after being molten rock. There are the rocks that make it to the surface (extrusive) and the ones that are stuck in the crust just below the surface (intrusive). There are two basic types of igneous rocks. They come from the center of the Earth! Not really the center, but they often start their lives below the crust and then get pumped out. Igneous rocks are the ones that were superheated and originally liquid. Granite is a rock and quartz is a mineral. It's ground up and crushed, but its still bits of quartz. But a piece of granite often has loads of quartz. On its own (as a mineral) it's a nice pretty crystal. There's an easier example that many people can relate to. But the rock that surrounds that ruby has many many different compounds (and even a few pieces of ruby mixed in). It's a nice pretty crystal with the same compounds throughout the object. They don't have easy chemical formulas to describe their makeup. Rocks are groups of different minerals pushed together and combined. Let's start off with an explanation that rocks and minerals are different things.
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